Conventionally, there is known a navigation system for guiding the way to a specified destination by finding the path to the destination. Such a navigation system includes a storage device, a pathfinding process unit, and a forecast process unit. The storage unit stores pathfinding data, map data including information regarding areas, and traffic information. The pathfinding process unit finds plural paths to the destination, and if any of the paths passes through a predetermined area, a forecast passing time is calculated for a link within the predetermined area. Based on traffic information, the forecast process unit creates forecast traffic information corresponding to the forecast passing time for the link within the predetermined area (see patent document 1).
The navigation system creates forecast traffic information after calculating the forecast passing times for all of the links within the predetermined area, and therefore the optimum path can be presented to the driver, in consideration of the ever-changing traffic congestion conditions.
Patent Document 1: Japanese Laid-Open Patent Application No. 2006-17610
However, in the navigation system described in patent document 1, as the number of predetermined areas or the number of links in a predetermined area increases, the amount of calculation operations increases for obtaining the forecast passing times. Consequently, the calculation workload on the control device increases.
Accordingly, there is a need for a navigation device capable of presenting an appropriate path to the driver in consideration of the ever-changing traffic congestion conditions, with reduced calculation workload.